Abstract

Plant cells require considerable transcriptional reprograming to mount an effective response to pathogens. Plant responses to pathogens have to be finely balanced with other vital biological processes such as development and growth. A major mechanism controlling the modulation of gene expression is chromatin remodelling. Chromatin remodelling requires histone covalent modifications and/or the action of ATP- dependent remodelling complexes. The combined action of these determine the accessibility of transcription factors and the basal transcription machinery to DNA and therefore greatly impact gene expression. There are several examples of histone modifying and chromatin remodelling enzymes previously shown to regulate plant development and immunity. This thesis explored the role of chromatin in plant defences, and how chromatin remodelling forms an integral part of the defence response.

Chapter 1 aimed to discover a “hidden” signal of chromatin marks in plant defence-responsive genes using an array of bioinformatics techniques. Subsequently, histone H3K27 tri- methylation (H3K27me3) was identified as a mark associated with gene repression at defence-related loci. The role of histone H3K27me3 and its associated histone demethylase enzymes REF6 and ELF6 were empirically characterised.

Chapter 2 is dedicated to a reverse genetics screening investigating the role of the chromatin remodelling ATPases Arabidopsis family in plant defences, and describes the most prominent phenotypes.

And lastly, Chapter 3 dissects in greater detail the role of the chromatin remodelling ATPase EDA16 in plant defence. Pathogen assays, RNA-seq and other molecular techniques suggest that EDA16 is a negative regulator of immunity induced upon pathogen perception to regulate the amplitude of defence responses.